The aim of the study was to investigated in skeletal muscle the
expression, localization and possible function of P2X4 receptor, an
extracellular ATP-operated channel mainly permeable to Ca2+. By
RT-PCR and Western blot analysis we have demonstrated that P2X4
is expressed in several rat tissues, including skeletal muscle. A specific
antibody detected a protein band of about 60 kDa whose level was
higher in slow-than in fast-twitch muscles. P2X4 receptor is highly
glycosylated because digestion with N-glycosidase F reduced the mass
of the 60-kDa protein to about 45 kDa. Confocal immunofluorescence
in longitudinal sections revealed that P2X4 receptor is transversally
distributed and co-localized with the DHP receptor. This finding
indicates that P2X4 decorates T-tubule membranes and raises the
possibility that this ATP-gated cation channel may contribute to ECcoupling
of skeletal muscle. In vitro experiments showed that stimulation
of muscle fibers evokes the release of ATP, while tension
recordings evidenced an ATP-dependent potentiation of contractility,
particularly in fast-twitch muscles.
The financial support of TELETHON ITALY (grants n. 1286) is
gratefully acknowledged
